The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is driven by several turbojet engines, each being housed in a nacelle also housing a set of secondary actuating devices related to its operation and performing various functions when the turbojet engine is operating or stopped. These secondary actuating devices comprise in particular a thrust reverser actuating mechanical system.
A nacelle generally presents a tubular structure comprising an air intake upstream to the turbojet engine, a middle section designed to surround a fan of the turbojet engine, a downstream section comprising thrust reverser means and designed to surround the combustion chamber of the turbojet engine, and is usually completed by a nozzle of ejection the output of which is located downstream to the turbojet engine.
The modern nacelles are designed to house a turbojet engine with double flows able to generate, through the blades of the rotating fan, a flow of hot air (primary flow) and a flow of cold air (secondary flow) which circulates outside the turbojet engine through an annular passage, also called vein, formed between a fairing of the turbojet engine and an internal wall of the nacelle. The two air flows are ejected from the turbojet engine by the back of the nacelle.
The role of the thrust reverser is, when landing an aircraft, to improve its braking capability by redirecting to the front at least part of the air ejected by the turbojet engine. In this phase, the thrust reverser blocks at least a part of the vein of the cold flow and redirects this flow towards the front of the nacelle, thereby generating a counter thrust which is added to the braking of the wheels of the aircraft.
A common structure of a thrust reverser comprises an enclosure wherein is provided an opening designed for the diverted flow, which, while operating as a direct jet of the nacelle, is closed by an external cowl and which, while operating as reverse jet of the nacelle, is opened by displacement in a downstream translation (by reference to the direction of the gas flow) of the external cowl, by means of displacement cylinders of the external cowl, said displacement cylinders being mounted on a frame of the enclosure upstream to the opening.
The external cowl is often formed by two half-cowls having an essentially semi-cylindrical shape, which are articulated in the upper part (so-called at 12:00 position) on hinges significantly parallel to the direction of translation of the external cowl, and which are closed by locks on the bottom part (called at 6:00 position).
This disposition allows, for maintenance operations, accessing inside the nacelle, and particularly to the turbojet engine or to an internal structure of the reverser by opening these half-cowls.
In order to solve some problems related to such a ‘Butterfly’ opening, an opening in translation solution has been developed and is particularly described in French Patent Appln. No FR 2 911 372. This application describes a structure of a thrust reverser comprising an external set into one single part, in other words, without closing in the lower part. Such a structure is called monoblock structure or O-shaped structure.
French Patent Appln. No. FR 2 952 681 also describes an O-shaped structure comprising a thrust reverser with fixed cascades while operating of the nacelle in direct jet or in reverse jet, and the whole set of which is formed by the external cowl and the cascades translate during maintenance operations, allowing easier access to the engine. Deflecting cascades are connected to the fan housing by their front frame and the disconnection of the front frame from the fan housing is necessary when reaching the engine during maintenance operations is desired.
Disadvantages associated with these solutions lie in the complexity of the disconnection system between the front frame of the cascades and the fan housing. Indeed, the disconnection of the cascades attached to the fan housing is complicated manually because access to the system of disconnection is restricted. On the other hand, such an opening system for the maintenance operations requires an opening system separate from that used to open the external cowl during an operation in reverse jet of the nacelle, which greatly increases the weight of the nacelle and goes against solving the problem of reduction of weight, recurring in aeronautics.
Besides, another recurring problem related to the nacelles for turbojet engine is that the dimensions of the nacelle and of the associated cowl are too important, leading to increases in drag.
Indeed, the length of the cascades necessary to the deflection of flow is determined by the cold flow rate. Because of aerodynamic constraints, they also occupy a certain volume within the thrust reverser cowl what can generate important dimensions of the reverser cowl and the nacelle.
There is thus a need to limit the dimensions of the cowl and of the nacelle and, consequently, to reduce the mass and the drag of the latter.